Conventional synthetic fibers made of synthetic resins are slow in rate of degradation under natural environment and generate a large amount of heat at burning and, therefore, have to be reconsidered from the viewpoint of environmental protection. For such a reason, spontaneously degradable fibers made of aliphatic polyesters are being developed, and their contributions to environmental protection have been expected. However, these spontaneously degradable aliphatic polyester fibers are not satisfactory in bulkiness, softness, feeling and so on, and an improvement thereof has been desired.
Conventionally it is known that goods such as knitted and woven fabrics having excellent bulkiness and softness are obtained if fibers having a different shrinkability are combined in usual inter-fiber composites (blends of fibers). However, as to aliphatic polyester fibers having a spontaneous degradability, a manner of controlling the shrinkability has been scarcely known so far and, of course, it is not known at all to conjugate fibers having a different shrinkability and to improve the quality of knitted fabrics and woven fabrics by using it.
Also, in order to obtain a fiber having a high softness and various functions based on a special shape of section and a large surface area, it has been conventionally practiced to divide a dividable conjugated fiber. By this method, there have been developed and widely used knitted and woven fabrics, non-woven fabric, artificial leather, artificial suede, high performance wiping cloth, high performance filter and so on. However, in the field of degradable fibers in natural environment, no dividable conjugated fiber has been proposed. The reason is that combination of spinning materials (polymers) suitable for division and how to divide have not yet been known.
A self-adhesive (melt-adhesive) fiber that a part of a fiber melts by heating to adhere fibers to each other, has been widely used in the field of synthetic fibers. Melt-adhesive fibers using an aliphatic polyester are proposed in Japanese Patent Publications Kokai No. 6-207320 and Kokai No. 6-207324. However, in working examples thereof, a conjugated fiber composed of a sheath (adhesive component) of a polyethylene succinate having a melting point of 102.degree. C. and a core (strength-retaining component) of a polybutylene succinate having a melting point of 118.degree. C. is only disclosed, and the adhesive strength thereof is not so strong. The reason is that the difference in melting point between both components is as small as only 16.degree. C. and the strength-retaining component is softened and deteriorated by heating for adhesion. Also, the optimum temperature for adhesion treatment of this fiber is limited within a very narrow range, so it is very difficult to exhibit desired adhesive force and strength. It is also very difficult to alter the adhesive strength in a wide range according to the purposes, so the uses are limited. In general, a low-melting component has been used for the adhesive component of melt-adhesive fibers. However, if a low-melting aliphatic polyester having a melting point of not more than 120.degree. C. is used, the glass transition temperature is lower than ordinary temperature, so the solidifying rate is slow and, therefore, there arise many problems in practical use such that fibers are easy to stick to each other at the time of melt-spinning, so not only production at a high speed is difficult, but also the heat resistance in use is low.
An object of the present invention is to provide a spontaneously degradable fiber excellent in bulkiness, softness, feeling and stretchability, and textile goods prepared therefrom.
A further object of the present invention is to provide a spontaneously degradable fiber having a self-crimpability.
A still further object of the present invention is to provide a self-crimpable fiber which is spontaneously degradable, which reveals an excellent crimp by heating or the like so as to be able to provide goods excellent in softness, bulkiness and stretchability and, moreover, which can be easily prepared in high efficiency.
Another object of the present invention is to provide a conjugated fiber which is spontaneously degradable, which has an improved dividability and which can provide fibers and fiber structures having an excellent softness and a large surface area.
A still another object of the present invention is to provide a self-adhesive fiber which is spontaneously degradable, which exhibits an excellent adhesion property by heat treatment for adhesion and, moreover, has an excellent strength because of less deterioration of a strength-retaining component, which can be prepared by melt-spinning at a high velocity, and which can easily produce adhesive fiber structures having an excellent heat resistance, and to provide a fiber structure using it.
A further object of the present invention is to provide a self-adhesive fiber which is spontaneously degradable and which can be subjected to adhesion treatment within a wide temperature range and can widely alter the adhesive strength according to the purposes.
A still further object of the present invention is to provide a fibrous bulk material which is spontaneously degradable and is composed of a mixture of a plurality of fibers which show a different shrinkability by heating or the like, thus producing a difference in length between the fibers by heating, and accordingly which can provide goods excellent in bulkiness, softness and feeling.